1. Technical Field
The present invention relates to an imaging device, a defocus amount calculating method, and an imaging optical system.
2. Related Art
Recently, as the resolution of a solid state imaging element such as a charge coupled device (CCD) image sensor and a complementary metal oxide semiconductor (CMOS) image sensor becomes higher, a demand for an information device having an imaging function such as a digital still camera, a digital video camera, a cellular phone such as a smart phone, and a personal digital assistant (PDA) is rapidly increasing. Further, the information device having an imaging function as described above is referred to as an imaging device.
In such an imaging device, as a focus control method which detects a distance to a major subject to focus on the major subject, a contrast auto focus (AF) method or a phase difference AF method is employed. Since the phase difference AF method may detect a focusing position at a high speed as compared with the contrast AF method, the phase difference AF method is widely employed in various imaging devices (for example, see Patent Literatures 1 to 3).
Patent Literature 1 (JP-A-2010-26178) discloses an imaging device which has some of the pixels included in an imaging element as a phase difference detecting pixel and performs the phase difference AF using a signal read out from the phase difference detecting pixel. Patent Literature 1 discloses that a gain difference is caused between a pair of image signals which are targets for calculating a phase difference, due to lens vignetting and a method which corrects the gain difference based on a pixel output ratio distribution in each pixel of the pair of image signals whose phases match.
Further, Patent Literature 2 (JP-A-2010-107771) and Patent Literature 3 (JP-A-2008-275712) disclose an imaging device which corrects data which causes degradation of phase difference AF precision, using a correction value generated for every lens and then performs phase difference AF so as to improve AF precision.